Multipurpose Internet Mail Extensions (MIME)

Recently, the Internet Engineering Task Force (IETF) has developed a document titled "Multipurpose Internet Mail Extensions" or MIME, RFC-1341, RFC-1341 and 1342 RFC-1342.

MIME is the official proposed standard format for multimedia Internet mail encapsulated inside standard Internet RFC 822 messages. Facilities include sending multiple objects in a single message, character sets other than US-ASCII, multi-font text messages, non-textual material such as images and audio fragments, and other extensions.

MIME defines structure for Internet message bodies through enhancements to the Content-Type field.

In MIME, the term "content-type" is used to refer to an information object contained in the body of a message.

RFC 1341 covers only message bodies, not message headers; to see how to represent non-ASCII characters in message headers, see Internet RFC 1342: K Moore, "Representation of non-ASCII text in Internet message headers" (June 1992).

MIME, the Multi-purpose Internet Mail Extensions, is a freely available specification that offers a way to interchange multi-media e-mail among many different computer systems. MIME supports not only several pre-defined types of non-textual message contents, such as audio, GIF files and PostScript images, but also permits you to define your own types of message parts.

Pre-Defined MIME Types  

Each part of a multimedia message identifies what type of information is carried in the message part. For example, a message part containing audio data might have either type audio/basic or type audio/x-next. Both are audio types; the subtypes are basic and x-next.

An entire MIME message--as opposed to an individual part of a multipart message--can also have a type. For example, a message might have the type text/plain, and consist entirely of plain text. A MIME message containing parts of different types has the umbrella type multipart/mixed.

Here are brief summaries of the pre-defined types and subtypes in MIME version 1.0.

application/octet-stream

is for "other" kinds of data, either uninterpreted binary data or information to be processed by a mail-based application.

application/postscript

is for PostScript programs (typically documents represented in PostScript form).

audio/basic

is for audio data encoded using 8-bit ISDN (Pulse Code Modulation). A sample rate of 8000/second and a single channel is assumed.

image/gif

is for GIF (graphical interchange format) image data.

image/jpeg

is for JPEG (joint picture experts group) image data.

message/external-body

is for specifying large bodies by reference to an external data source.

message/partial

is for partial messages, to permit the fragmented transmission of bodies that are thought to be too large to be passed through mail transport facilities.

message/rfc822

is an encapsulated RFC 822 conformant message which may have its own type.

multipart/alternative

represents the same data in multiple formats.

multipart/digest

is for multipart entities in which each part is an encapsulated message.

multipart/mixed

is the primary way to represent a MIME message containing parts of various different types.

multipart/parallel

is for data intended to be viewed simultaneously.

text/plain

indicates plain (unformatted) text.

video/mpeg

is for MPEG (motion picture experts group) video data. Video requires the capability to display moving images, typically including specialized hardware and software.

RFC 1341, RFC-1341, contains more detailed explanations of required or optional attributes to be used with particular types.